This application is based on Japanese Patent Application Nos 11-238794 (1999) filed Aug. 25, 1999 and 2000-70872 filed Mar. 14, 2000 in Japan, the contents of which are incorporated here into by reference.
1. Field of the Invention
The present invention relates to an optical packet routing system for routing an optical signal by using the optical label signal carrying the control information necessary for the routing of the optical signal, more particularly, to a multiple-wavelength optical source unit to be used for a network system whose a plurality of communication nodes are connected by the wavelength routing system and an optical communication unit and an optical communication method to be used for an optical communication system whose internode communication among the communication nodes is made through a routing unit.
2. Description of the Related Art
With the explosive spread of the internets, and portable personal telephones and the like, the research and development activities for the establishment of large-capacity network are under way both at home and abroad. With the communication nodes constituting each of the existing networks, an optical signal transmitted through an optical fiber transmission line is converted into an electric signal; an address information and the like carried by the signal is read out; the signal is electrically switched to a desired output port according to the information; the signal is converted into an optical signal at the output port; and the optical signal is then transmitted through the optical fiber transmission line. However, with the exponential-growth in the communication traffic, in the near future, the routing processing capacity by the electrical routing processes is considered to reach its limit. To overcome this problem, it is important for the communication nodes to establish a routing method for enabling the routing of the signal within the optical layer, that is, a routing method for enabling the routing without converting the optical signal into the electric signal.
As a technique for realizing the above goal, the wavelength routing technique is coming to the fore. In the case of the wavelength routing technique as schematically illustrated in FIG. 1, any optical signal fed into a given input port can be routed selectively to different output ports according to its wavelength without being converted into an electric signal, by using an optical device (e.g., arrayed-waveguide grating) having a wavelength selectivity.
FIG. 2 schematically illustrates the general composition of the network system interconnecting a plurality of communication nodes by utilizing the wavelength routing function of the cyclic-wavelength arrayed-waveguide grating. In the case of this network system, with a cyclic-wavelength arrayed-waveguide grating 60 having a wavelength routing processing function, the optical signal transmitted from a communication node is routed in the form of the light according to its wavelength without undergoing any electrical processing for routing, so that high-speed routing is possible.
To illustrate the composition of FIG. 2, the network system comprises N number of communication nodes 30 (communication nodes #1-N) and a cyclic-wavelength arrayed-waveguide grating 60 having a wavelength routing processing function. Each communication node 30 comprises transmitter equipment 40 and receiver equipment 50. The transmitter equipment 40 comprises N number of optical sources 41 for transmitting optical signals having wavelengths xcex1-xcexn.
The optical signals (wavelength: xcex1-xcexn) transmitted from the transmitter equipment 40 of each communication node 30 are introduced into the input ports of the cyclic-wavelength arrayed-waveguide grating 60 having the wavelength routing processing function. The cyclic-wavelength arrayed-waveguide grating 60 routes the optical signals incoming from various communication nodes 30 to different output ports according to the wavelengths, xcex1-xcexn, of the optical signals. Since this routing processing of the optical signal is carried out according to the wavelength of the optical signal while maintaining the form of the light without being subjected to any electrical processing, the high-speed routing is possible.
The optical signals (wavelength: xcex1-xcexn) came out from the output ports of the cyclic-wavelength arrayed-waveguide grating 60 is introduced into the receiver equipment 50 in each communication node 30.
The detail of the wavelength routing processing by the cyclic-wavelength arrayed-waveguide grating 60 will be described referring to FIG. 3. Optical signals (wavelength: xcex1-xcex4) varying in wavelength transmitted from various communication nodes (#1-#4) are fed to the input ports 61a-61d of the cyclic-wavelength arrayed-waveguide grating 60. In this case, the optical signal transmitted from the communication node #1 to the input node 61a is outputted from the output port 62a when its wavelength is xcex1, from the output port 62b when its wavelength is xcex2, from the output port 62c when the wavelength is xcex3 and from 62d when the wavelength is xcex4.
The optical signal to be transmitted from the communication node #2 to the input port 61b is outputted from the output port 62d when its wavelength is xcex1, from the output port 62a when its wavelength is xcex2, from the output port 62b when its wavelength is xcex3, and from the output port 62c when its wavelength isxcex4.
The optical signal to be transmitted from the communication node #3 is outputted from the output port 62c when its wavelength is xcex1, from the output port 62d when its wavelength is xcex2, and from the output port 62a when its wavelength is xcex3, and from the output port 62b when its wavelength is xcex4.
The optical signal to be transmitted from the communication node #4 to the input port 61d is outputted from the output port 62b when its wavelength is xcex1, from the output port 62c when its wavelength is xcex2, from the output port 62d when its wavelength is xcex3, and from the output port 62a when its wavelength is xcex4.
Thus, by the routing to be carried out as described above, the optical signals having the same wavelengths respectively transmitted from the communication nodes #1-#4 will never be outputted from the same output port. In other words, the wavelength routing by using the cyclic-wavelength arrayed-waveguide grating as is shown in FIG. 3 is characterized by that the optical signals having the same wavelengths fed to different input ports of the grating are outputted from different output ports of the grating respectively, so that the conflict among the data having the same wavelengths with respect to the output port can be prevented.
However, in the case of conventional network system as is shown in FIG. 2, especially in the case of the network comprising N number of communication nodes, it is necessary to provide N number of optical sources with wavelengths strictly adapted to the wavelength characteristic of the cyclic-wavelength arrayed-waveguide grating with respect to each of the communication nodes and thus requiring Nxc3x97N number of optical sources, which is a problem to be resolved. Especially, providing N number of optical sources for each communication node not only results in the increase in the burdens such as the increase in the size and cost of the communication node but also results in the increase in total cost of the network system.
Next, a prior art relating to the second embodiment of the present invention will be described.
Conventionally, as an optical communication system for carrying out the optical communication among a plurality of communication nodes through a router, a system shown in FIG. 4 has been available.
The communication nodes 100a-100d are respectively provided with one of the corresponding optical signal transmitters 71a-71d for respectively transmitting one of the corresponding optical signals 76a-76d and also respectively provided with one of the corresponding optical label signal transmitters 72a-72d for respectively transmitting one of the corresponding optical label signals 77a-77d carrying the control information necessary for the routing of the optical signal.
The routing device 80 is connected respectively to each communication nodes 100a-100d through the corresponding optical transmission lines 81a-81d and comprises wavelength demultiplexers 74 for separating the optical signals and the optical label signals, optical receivers 78e for receiving the optical label signals separated by the wavelength multiplexers 74, optical splitters 79 for branching the optical signals separated by the wavelength demultiplexers 74 to a plurality of optical paths and a plurality of optical gates 75a-75d for selecting the optical path by the routing processing for passing or intercepting the optical signals according to the control information in the optical label signals 77a-77d respectively connected to a plurality of the corresponding optical paths. The control circuit section for controlling the optical gates 75a-75d are not shown in the figure.
When the optical signals 76a-76d and the optical label signals 77a-77d respectively including the control routing information of the optical signals are fed respectively to the router 80 through the optical transmission lines 81a-81d after being transmitted respectively from a plurality of communication nodes 100a-100d (the four communication nodes #1-#4 in the case shown in the figure), the optical signals 76a-76d and the optical label signals 77a-77d are respectively separated by the wavelength demultiplexers 74 provided in the router 80 respectively corresponding to the communication nodes.
Further, the optical signals 76a-76d are respectively branched by the optical splitter 79 in the stage following the wavelength demultiplexer 74 and respectively introduced into the corresponding optical gates (three optical gates among the optical gates 75a-75d in the case shown in the figure) through a plurality of optical paths of substantially the same length (three optical paths in the case shown in the figure). On the other hand, the optical label signals 77a-77d are respectively guided to the corresponding optical receivers 78e. Next, when the optical signal passes one or a plurality of optical gates among a plurality of optical gates 75a-75d, which is or are designed to be driven according to the information carried by the optical label signal received by the optical receiver 78e, the optical path for the optical signal is selected from among the optical paths 82a-82d. 
The time required for the optical signal 76 (the representative number of 76a-76d) to arrive at the optical gate 75 (the representative number of 75a-75d) from the input port of the wavelength demultiplexer 74 of the router 80 is given a t1; the time required for the optical label signal 77 (the representative number of 77a-77d) corresponding to the optical signal 76 to arrive at the optical receiver 78e from port of the wavelength demultiplexer 74 is given as t2; the time required for the optical receiver 78e to drive the optical gate 75 (to permit the optical signal to pass) after completing the reception of the optical label signal 77 is given as t3. Under these conditions, in the optical gate 75, in order for the optical signal 76 to be processed for proper gating, it is necessary for each of the communication nodes 100 (the representative number of 100a-100d) to output both the optical signal 76 and the optical label signal 77 respectively with a time lag so that the time lag becomes equal to the relative time Txe2x80x2 (the time lag between the front of the optical signal 76 and the end of optical label signal 77 arrived at the input port of the wavelength demultiplexer 74, denoted by numeral 90 in FIG. 5) to satisfy the inequality (1) given below.
xe2x80x83Txe2x80x2 greater than t2+t3xe2x88x92t1xe2x80x83xe2x80x83(1)
On the other hand, in order to raise the data communication efficiency among the communication nodes 100, as shown in FIG. 6, it is necessary to adjust the relative time lag Txe2x80x2 in the above inequality (1) so that the time lag xcex94t (denoted by numeral 91) between the arrival time of the optical signal 76 at the optical gates 75 to drive the optical gates 75 and the time (denoted by numeral 92) at which the optical signal is allowed to pass is reduced as far as possible.
By predetermining the values of t1, t2 and t3 in the above inequality (1), the relative time lag Txe2x80x2 between the optical signal 76 and the optical label signal 77, which is necessary for proper gating of the optical signal 76 by the optical gate 75, can be determined.
However, in general, in the case of the optical communication system by using the optical label signal, for the easy separation of the optical signal and the optical label signal by the router 80, these signals have different wavelengths. Therefore, the relative time lag between the optical signal and the optical label signal varies according to transmission distance due to the effect of the wavelength dispersion of the optical fiber which is a transmission medium of the optical signal. In consequence, the time lag T between the transmission of the optical signal and that of the optical label signal set by the communication node 100 differs from the relative time lag Txe2x80x2 at immediately before the input port of the wavelength demultiplexer 74 of the router 80. Since the distances from various communication nodes 100 to the router 80 vary, it is necessary to adjust the transmission time lag T between the transmission of the optical signal and that of the optical label signal so that the relative time lag Txe2x80x2 for each of the communication nodes 100 satisfies the above inequality (1).
However, since the router and each communication node are, in general, arranged at physically separated locations, when setting the previously mentioned transmission time lag T at each communication node, it is necessary to adjust in real-time conjunction so that the data is transmitted properly to each communication node, but this process is very cumbersome in the case of the conventional system.
The present invention has been made in consideration of the problems of the related arts, and from a new viewpoint that is not expected in the conventional methods.
Thus, it is the first object of the present invention concerning the first embodiment of the present invention to provide an optical communication device capable of resolving the previously mentioned problem of the conventional wavelength routing by drastically reducing the number of optical sources necessary for each communication node by providing shared optical sources to be shared among a plurality of communication nodes so that the number of required optical sources in each of the communication nodes is reduced and each of the communication nodes is not required to be provided with its own optical source having the wavelength strictly adjusted for data transmission.
Further, another object relating to the first embodiment of the present invention is to provide an optical communication device capable of forming a simple system not requiring each communication node to be provided with its own optical sources having its wavelength strictly adjusted for data transmission.
In order to achieve the above object, a multi-wavelength optical source equipment employed for an optical network system with a plurality of communication nodes connected with one another by a wavelength routing method and for converting the wavelength of the optical signals to desired wavelengths so as to transmit to desired communication nodes, the optical signals carrying the control information concerning the routing of the signals from each of the communication nodes, comprising: first optical splitters for branching the optical signals transmitted from each of the communication nodes to a first optical path and a second optical path; optical receivers for receiving the optical signals that have passed the first optical path; second optical splitters for branching the optical signals that have passed the second optical path to a plurality of optical paths; a plurality of optical gates for passing or intercepting the optical signals branched by the second splitters; wavelength converters for converting the wavelength of the optical signals outputted from the optical gates into desired wavelengths; a controller for controlling optical gates according to the control information relating to the routing of the optical signals received by the optical receivers; optical delay devices for adjusting the optical path length so that the optical signals that have passed the second optical path will not enter the optical gates before the optical gates are driven by the controller; multi-wavelengths optical sources for supplying the light having desired wavelength to each of the wavelength converters; and wavelength multiplexers for multiplexing the optical signals whose wavelengths have been converted by the wavelength converters.
It is the second object of the present invention concerning the second embodiment of the present invention to provide an optical communication system and an optical communication method for enabling individual communication nodes to self-supportingly adjust the transmission time lag T between the optical signal and the optical label signal for the optical signal so as to prevent the loss of the part or all of the optical signal by way of each optical signal transmitted from each communication node to pass the optical gates of the router by inappropriate timing, thereby realizing a marked reduction of work load relating to the setting of the transmission time lag T at each communication node.
In order to achieve this object, according to the present invention, an optical communication equipment comprising: a plurality of communication nodes having an optical signal transmitter for transmitting the optical signals and an optical label signal transmitter for transmitting the optical label signals carrying the control information concerning the routing of the optical signals respectively, for transmitting the optical signals and the corresponding optical label signals giving a relative transmission time lag; a router having wavelength demultiplexers connected to each of the communication nodes through the optical transmission line for separating the optical signals from the optical label signals, optical label signal receivers for receiving the optical label signals separated by one of the wavelength demultiplexers, optical splitters for branching the optical signals separated by one of the wavelength demultiplexers to a plurality of optical paths of a substantially the same length, a plurality of optical gates for routing by passing or intercepting the optical signal with respect to a corresponding optical path of the a plurality of optical paths according to the information carried by the optical label signal received by one of the optical label signal receivers; each of the communication nodes comprises: an optical signal transmission means for transmitting the optical signals addressed to the communication node that transmitted it through the optical transmitter; an optical label signal transmission means for transmitting the optical label signal carrying the routing information of the optical signal through the optical label signal transmitter; an optical receiver for receiving the optical signal addressed to the communication node that transmitted it and returned through the router; a diagnosing means for diagnosing the optical signal received by the optical receiver; and an adjusting means for adjusting the transmission time lag between the optical signal and the optical label signal according to the result of the diagnosis by the diagnosing means.
In order to achieve the second object, according to the present invention, an optical communication method for optical communication by using the a plurality of communication nodes for transmitting the optical signal and optical label signal with relative transmission time lag and an optical router for passing or intercepting the optical signal according to the control information carried by the optical label signal, comprising the steps of: transmitting from each communication node an optical signal addressed to the communication node that transmitted it and the corresponding optical label signal giving a relative transmission time lag; receiving from each communication node the optical signal addressed to the communication node that transmitted it through the router; testing whether the optical signal addressed to the communication node that transmitted it has been received without an error or not; and setting the transmission time lag between the optical signal addressed to the communication node that transmitted it and the corresponding optical label signal according to the result of the test so that the optical signal addressed to the communication node that transmitted it is received without an error, and the transmission time lag set in this way is set as the transmission time lag between the optical signal and the corresponding optical label signal with respect to the corresponding communication node.
In the network system according to the first embodiment of the present invention where a plurality of communication nodes are connected by means of the wavelength routing method, multi-wavelength optical source equipment, having shared multi-wavelength optical sources and a wavelength conversion function, is provided between each the communication node and the wavelength router and is shared by each communication node.
With this arrangement, in the case of the first embodiment of the present invention, the wavelength of the optical signals transmitted from each communication node can be converted into the wavelengths adapted for routing to desired communication nodes by using the light provided from the shared multi-wavelength optical sources, whereby for a plurality of communication nodes interconnected by the wavelength routing system, the number of the optical sources for the data transmission provided for each communication node, which results in the building of a low-cost system.
Further, in the first embodiment of the present invention, the wavelength of the principal optical signals transmitted from each communication node are converted into the wavelengths necessary for the wavelength routing by the multi-wavelength optical source equipment, so that it is not necessary to provide optical sources having strictly defined wavelength for each communication node, thereby making easier the system configuration.
Further in the first embodiment of the present invention, though the transmission bit rate of the data increases, it is possible to reduce the load of the electrical processing for reading the routing information of the data by transmitting the routing information of the data with a low bit-rate optical signal having the wavelength differing from the data signal.
Further, in the case of the first embodiment of the present invention, the status information of data transmissions from the communication nodes can be converged to the multi-wavelength optical source equipment, so that the control of the network can be made easier.
According to the second embodiment of the present invention, each of the a plurality of nodes sends out the optical signal (optical signal addressed to the communication node that transmitted it) and the corresponding optical label signal to the router; the optical signal addressed to the communication node that transmitted it is made to pass the optical gate of the router according to the control information of the optical label signal and returned to the communication node that transmitted the optical signal; the communication node examines the optical signal addressed to the communication node that transmitted it after receiving the optical signal and adjusts the transmission time lag between the optical signal and the corresponding optical label signal so that the optical signal can be received correctly.
By doing so, according to the second embodiment of the present invention, the transmission time lag T between the optical signal and the corresponding optical label signal can be adjusted self-supportingly by each communication node. Therefore, according to the second embodiment of the present invention, even in the case of an optical communication system wherein the optical path length between the router and each communication node differs case by case and the optical signal and optical label signal use different wavelength respectively, the optical signals sent out from each communication node are respectively made to pass the optical gates of the router by proper timing, thereby surely and easily preventing a part or whole of an optical signal from being lost due to the routing processing.
Further, according to the second embodiment of the present invention, the performance for setting the transmission time lag can be made easier and wild reduction for each communication node.
Therefore, the optical packet routing system by using the optical label signals according to the present invention can be expected to be capable of contributing to the development of the optical communication systems such as Metropolitan Area Network (MAN), a communication carrier, Wide Area Network (WAN), those for business enterprises, those for universities such as the campus area networks and the like.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.